1. Field of the Invention
The invention relates to a driver circuit, more particularly to an electric lighting driver circuit.
2. Description of the Related Art
As shown in FIG. 1, a conventional in-vehicle electric lighting driver circuit 1 is electrically connected to an in-vehicle power source V1 and a high intensity discharge (HID) lamp, and is for converting a direct current (DC) input voltage from the in-vehicle power source V1 to an alternating current (AC) low frequency, rectangular wave voltage to drive the HID lamp. The in-vehicle electric lighting driver circuit 1 includes a flyback DC-to-DC converter 11 and a full-bridge DC-to-AC converter 12. The flyback DC-to-DC converter 11 is configured to boost the DC input voltage so as to provide a high DC voltage that is stable and that has relatively small ripples, and includes a power switch S, a single-output winding transformer 111 and an output diode D. The power switch S is operated at a high frequency to boost the DC input voltage to the high DC voltage.
The full-bridge DC-to-AC converter 12 is electrically connected to the flyback DC-to-DC converter 11 and the HID lamp, and includes an output capacitor C1 and four power switches, namely S1, S2, S3 and S4. The power switches S1, S2, S3 and S4 are operated at a low frequency, in order to convert the high DC voltage to a low frequency, rectangular wave voltage that is necessary for the HID lamp to operate in a steady state.
Nonetheless, the full-bridge DC-to-AC converter 12 requires four power switches, raising the manufacturing costs of the electric lighting driver circuit 1. Moreover, FIG. 2 illustrates an extended structure of the conventional electric lighting driver circuit 1 depicted in FIG. 1, which is adapted to drive two HID lamps. Compared to the original structure, the extended structure employs an additional output capacitor C2 and four additional power switches S5, S6, S7 and S8, bringing the manufacturing costs even higher.